1. Field of the Invention
The present invention relates to a method for transmitting mechanical energy between a transfer piston of a Stirling machine and a moveable member of a generator or of an electric motor, the transfer piston being mounted in a cylinder, according to which a working gas is periodically displaced between an expansion chamber and a compression chamber with the aid of said transfer piston, said chambers being associated respectively with two working faces of said transfer piston, by making said gas pass through a hot, alternately cold exchanger linked to a heat source, a regenerator and a cooling exchanger linked to a heat sink, and an elastic restoring force is exerted on this transfer piston.
2. Description of the Related Art
Free-piston Stirling machines have long been regarded as an ideal solution for heat/force coupling units serving for the production of thermal and mechanical energy for homes. The possibility of increasing the degree of use of fossil fuel, the cleanliness of the external combustion process and the quiet operation of the device constitute the main arguments in favor of the application of this technology to homes. However, up to now the complexity and high cost of such units have prevented their use.
It has recently been proposed to associate a driving piston with a transfer piston of a Stirling machine and to fix the field magnets of an electric alternator to this driving piston so as to displace them relative to the windings of the armature of this alternator. This promising concept has the drawback however of requiring two coaxial pistons, moveable with respect to one another, which must be guided with high accuracy. Specifically, the rod of the transfer piston is mounted slideably in a gas-filled closed volume of the driving piston, which pneumatically couples these two pistons. This system also requires servocontrol in such a way as to adjust the phase shift between these pistons. Such a system is developed by the American firm Sunpower Inc., Athens, Ohio, and is in particular the subject of an article entitled xe2x80x9cDevelopment of a 3 kW free-piston Stirling engine with the displacer gas-spring partially sprung to the power pistonxe2x80x9d, G. Chen and J. McEntee, Proceedings of the 26th Intersociety Energy Conversion Engineering Conference, vol. 5, p. 233-238. Strong elastic coupling between the two pistons indicates that a substantial fraction of the driving energy induced is produced by the forces of the gas acting on the transfer piston and transferred by the elastic linkage to the driving piston. The authors of the article affirm that ⅔ of the total energy is produced by the transfer piston of the Stirling engine. In this engine, this piston serves therefore not only to transfer the gas between the hot and cold volumes situated at the two ends of the cylinder in which this piston is displaced, but also to produce a part of the driving energy. 
Certainly, one could thereupon legitimately ask whether it would not be possible to produce all of the driving energy with the aid of the transfer piston and to associate the moveable part of the electric generator with the latter. Such an assumption by itself would not however solve the abovementioned problems. Specifically, since the phase shift required between the two coaxial pistons is still necessary to allow the production of energy and its transfer, the problems of guidance and servocontrol would remain unchanged.
The aim of the present invention is to remedy, at least in part, the abovementioned drawbacks.
Accordingly, a subject of this invention is firstly a method for transmitting mechanical energy between a transfer piston of a Stirling machine and a moveable member of a generator or of an electric motor. A subject of this invention is also a device for implementing this method.
The replacing of the driving piston by a completely static pneumatic resonator makes it possible not only to considerably simplify the device, since this method makes it possible to dispense with the driving piston, but also to facilitate the servocontrol as will be explained subsequently. This signifies that not only does the invention make it possible to substantially simplify the device and to reduce the production costs thereof, but also that the reliability of the device is thereby increased. However, for such a device to have an economical benefit, not only must it be possible to produce it at a competitive price, but it must also be capable of operating for many years without requiring any servicing or adjustment.